1. Technical Field
The present invention relates to a technology which ejects a fluid from an ejection head.
2. Related Art
Ink jet printers today are widely used to output desired images by ejecting ink onto printing media to produce high quality printed image. The technology of ink jet printing can also be applied in various kinds of manufacturing processes of precision parts such as electrodes, sensors or biochips, by ejecting appropriately prepared fluid (fluid containing dispersed microparticles or semifluid such as gel, for example) onto substrates.
Specially designed ejection head provided with microscopic ejection ports is used to realize such accuracy in ejecting correct quantity of fluid onto a correct position. Drive elements (for example, piezoelectric elements) connected to the ejection ports of the ejection head operate in accordance with a voltage applied. Hence, appropriately controlling the voltage applied to the drive elements enables the control of the quantity of fluid being ejected.
When using piezoelectric elements as the drive elements, because they are capacitive loads, power supplied to the drive elements to raise the applied voltage is stored in the drive elements. If the power stored in the drive elements is recovered to capacitors as the voltage applied to the drive elements is lowered to be reused again for raising the voltage applied to the drive elements, it highly contributes to improving power efficiency. Although, if the voltage of the capacitors is significantly low with respect to the terminal voltage of the drive elements, a large current flows out from the drive elements to the capacitors once the recovery of the power is attempted, resulting in large power consumption. Yet, if the terminal voltage of the drive elements is too close to the voltage of the capacitors, not much of power in the drive elements can be recovered. JP-A-2003-285441 discloses capacitors with differing voltages connectable to the drive elements, in which the capacitors with higher voltages are connected to the drive elements until recovering of the power becomes difficult, then the capacitors are switched to those with lower voltages. It enables much of power to be recovered while avoiding the current flow.
However, JP-A-2003-285441 requires capacitors with differing voltages, corresponding power sources to charge the capacitors at different voltages, and much space to fit them all inside the device.